1. Field of the Invention
The present invention relates to a method and related communications device for improving discontinuous reception (DRX) functionality in a wireless communications system, and more particularly, to a method and related communications device for improving stop mechanism of a DRX Retransmission Timer of the DRX functionality in a wireless communications system.
2. Description of the Prior Art
The third generation mobile telecommunications system (called 3G system) provides high frequency spectrum utilization, universal coverage, and high quality, high-speed multimedia data transmission, and also meets all kinds of QoS requirements simultaneously, providing diverse, flexible, two-way transmission services and better communication quality to reduce transmission interruption rates.
Long Term Evolution wireless communications system (LTE system), an advanced high-speed wireless communications system established upon the 3G mobile telecommunications system, supports only packet-switched transmission, and tends to implement both Medium Access Control (MAC) layer and Radio Link Control (RLC) layer in one single communication site, such as in Node B alone rather than in Node B and RNC (Radio Network Controller) respectively, so that the system structure becomes simple.
Targeting on the present LTE system, Discontinuous Reception (DRX) functionality is applied to the MAC layer for allowing a user equipment (UE) to enter a standby mode during certain periods of time and stopping monitoring a Physical downlink Control Channel (PDCCH), so as to reduce power consumption of the UE.
In cases of using the DRX functionality, whenever a new DRX cycle begins, an On Duration Timer is started and the UE is awaked to monitor the PDCCH until the On Duration Timer expires. In addition, when a DRX Inactivity Timer or a DRX Retransmission Timer is started, the UE also monitors the PDCCH.
During the time when the UE monitors the PDCCH, if the PDCCH indicates the UE to receive or transmit a new transmission packet, the DRX Inactivity Timer is started or restarted for allowing the UE to continue monitoring the PDCCH, so as to prevent missing reception or transmission of following packets.
On the other hand, if the PDCCH indicates the UE to receive a packet but the packet cannot be decoded successfully on a Downlink Share Channel (DL-SCH), the MAC layer of the UE would perform a Hybrid Automatic Repeat Request (HARQ) process to request a retransmission of the packet. Since the UE would not receive any retransmission packet during a signaling round trip time (RTT) of the HARQ process, a HARQ RTT Timer is thus configured by the DRX functionality to allow the UE to enter into the standby mode during this round trip time. So the power consumption of the UE can further be saved.
After the HARQ RTT Timer expires, the DRX Retransmission Timer is started by the DRX functionality to awake the UE to start monitoring the PDCCH for dectecting the retransmission packet of the HARQ process. In such a situation, if the retransmission packet of the HARQ process is successfully decoded, the DRX Retransmission Timer is stopped. Otherwise, the DRX Retransmission Timer is kept running until expiration, at which time the UE enters into the standby mode again.
Please refer to FIG. 1, which illustrates operation of a DRX Retransmission Timer according to the prior art. As shown in FIG. 1, at time T1, if the PDCCH indicates the UE a downlink transmission of a HARQ process, the HARQ RTT Timer is started. Since no retransmission packets would be received by the UE when the HARQ RTT Timer is running, the UE can go to sleep on this period of time to save power consumption. After the HARQ RTT Timer expires, the DRX Retransmission Timer is started and the UE starts to monitor the PDCCH for detecting retransmission packets of the HARQ process.
Since the DRX Retransmission Timer is running, if the PDCCH indicates the UE another downlink transmission packet for the HARQ process at time T2, for example, the HARQ RTT Timer is started again. At this time, the DRX Retransmission Timer is still running. Thus, the UE is awake to monitor the PDCCH even though no retransmission packets for the HARQ process would be received by the UE when the HARQ RTT Timer is running, resulting in the power of the UE wastes unnecessarily.
In other words, during the operation of the DRX Retransmission Timer, the UE would not receive any retransmission packet of the concerned HARQ process in situations such as the HARQ RTT Timer is running. Thus, it is unnecessary for the UE to keep monitoring the PDCCH at this period of time.